Method and apparatus for



June s, 1943. `M A, RAMSEY 2,321,242

METHOD AND APPARATUS FOR CONDITIONING AIR Filed Nov. 14, 1939 PatentedJune 8, 1943 METHOD AND APPARATUS FR CONDITIONING AIR.

Melvin Atkinson Ramsey, Buenos Aires, Argentina Application November 14,1939, Serial No. 304,317 In Argentina `uly 6, 1939 (Cil ca -12s) 4Claims.

The present invention relates to air conditioning and in particular toair conditioning methods and apparatus in which a portion of therecirculated air is by-passed with respect to the air conditioningdevices.

It has been recognised for some time that the by-passing of a portionofthe main stream of recirculated air in such manner that the by-passedportion is not subjected to the action of the cooling and dehumidifyingdevices allows desirable conditions to be obtained which cannototherwise be achieved. According to known methods the proportion of airby-passed has been controlled by a variety of instrumentalities all ofwhich have been either directly or indirectly responsive to a factorpresent in the air in the conditioned space or in the return duct.Generally other means have been provided for maintaining constant thetemperature of the cooling medium by varying the degree of refrigerationthereof. In water cooled apparatus, the volume of cooling medium (water)available is generally such that the refrigerator can be satisfactorilyoperated by a thermostat device controlling the capacity of therefrigerator plant, because the relatively large Volume ofswater willallow the refrigerator to operate for reasonably long periods withreasonably long intervals. If, however, direct expansion coils are usedas the cooling medium, the system just described fails because thecapacity variations available in such a type of cooling anddehumidifying device are very limited in practice. Consequently thecontrol apparatus responsive to air conditions used to control theproportion of by-passed air to recirculated air will by varying thedemand of the cooling medium cause the capacity of one such coolingdevice to vary with considerable and objectionable frequency, or, ifmore than one com- .pressor is used to secure variation in therefrigeration capacity by cutting compressors in and out of circuit, theeffect of the aforementioned control apparatus will be to stop onecompressor are never met in practice.

in other words, a large number of compressors, so that the installationwould become disproportionately huge and expensive. Again, a directexpansion cooling plant composed of a small number of units could beefficiently controlled by known methods'provided that the cooling demandalways varied in steps substantially equal to the capacity of each unit,but such conditions As is well-known by-passing is used in the ar ofair-conditioning for a variety of objects, but fundamentally the purposeis essentially to dilute a volume of freshly conditioned air with avolume of air withdrawn from the conditioned space (recirculated air)but not subjected to conditioning before being reintroduced into theconditioned space, in orderto obtain the desired constancy of thetemperature and humidity factors in the conditioned space. Seasonal andother circumstantial variations call for adjustment of the proportion ofby-passed air to freshly conditioned air, particularly when the freshlyconditioned air includes a proportion of outside air. The humidityfactor is controlled principally by means of the cooling device whichactsto alter the water content of the air passing therethrough independence on the relation between the temperature of the said airandthe temperature of when the temperature of the refrigerant fallsslightly, thereby causing a rise in said temperature to occurimmediately, whereupon the control apparatus will again start thecompressor, probably only a few seconds after it has been stopped. Suchfrequent starting and stopping of the compressors is highly undesirable.

Theoretically, of course, it would be possible to adapt a directexpansion cooling plant so as to enable the known type of controlapparatus to be used. but such adaptation would involve providing a verylarge number of unit steps, or

the effective element of the cooling means. In a dehumidifying device inwhich the medium is water, a sufficient volume of medium isl generallyavailable or can readily be made available so as to render the deviceinsensitive to transitory alteratons in the aforesaid temperaturerelationship while keeping it sufliciently sensitive to changes whichdemand a readjustment of the treatment conditions. Thus on thesupposition that the installation comprises two sources of cooling waterin one of which provision is made,l for local refrigeration and that theconditions in the circulating air have demanded a change over to therefrigerated supply of water, there will, owing to the volume of coolingmedium, be a sufficient lag before equilibrium is again established orover-shot to prevent a demand Abeing made with undesirable rapidity forachange back to the original treatment conditions.

Heretofore the proportion of recirculated air to intensively dehumidiedand cooled air has been controlled in dependence on the temperature ofthe space to be conditioned, hereinafter called the room temperature,and the capacity of the cooling and dehumidifying medium has beenadjusted in accordance with ,the temperature variations therein. Asalready stated suc'h an "y arrangement is satisfactory in cases in whichthe response of the cooling medium to changes of capacity is relativelyslow as in water-cooling, but is unsuitable in practice when it isdesired to use direct expansion coils as the cooling medium. The settingof the recirculation dampers as determined by the device responsive toroom temperature may be and very frequently is such that the capacity ofthe cooling plant at the time when the setting is effected, isinsufficient to deal with the volume of air to be intensively cooled butthat the addition of the next step of capacity is excessive. In thesecircumstances, the undesirable conditions of rapid cutting in and out ofthe compressor motor associated with the additional step will prevail.

The known practice may therefore be summarized as consisting inoperating the recirculation dampers by means of a device responsive tothe room conditions in order to maintain the room temperature constant,and maintaining constant the temperature of the cooling medium byvarying the capacity of the refrigerator.

I have found, however, that the objections to which reference has beenmade may be overcome and substantially equal conditioning effectsachieved in an air conditioning plant in which direct expansion coilsIare used, if the capacity of the refrigerator be controlled inaccordance with variations in the room temperature and the dampers beoperated by a device responsive to a function of the surface temperatureof the refrigverator.

The room temperature will generally fluctuate at a very slow rate sothat the demands for extra capacity will not be frequent on this score.On the other hand, a device responsive to a function of the surfacetemperature of the refrigerator and arranged to control 'the dampers,can adjust the relative proportions of recirculated and conditioned airso as to maintain constant conditions in the room, without calling forchanges in capacity, at least until such a degree of disparity betweenthe conditions in the room and the setting of the capacity controllingdevice has arisen as to cause the latterto respond.

It is therefore the principal object of the present invention to providean improved method of air conditioning in which direct expansion coilsare utilised as the cooling medium; and in which f the cutting in andout with objectionable frequency of the compressor motors shall beavoided.

Another object of the present invention is to provide a method of airconditioning including the by-passing of air for recirculation withoutreconditioning, and the control of the proportion of by-passed air bymeans of dampers, in which direct expansion coils are utilized as thecooling medium and in which the settingof the dampers is controlled by adevice responsive to a function of the surface temperature oi saidcoils, the refrigeration capacity being controlled in response tovariations in the conditions in the air conditioned space.

A further object of the present invention is to provide a method of airconditioning including the by-passing of. air for recirculation withoutreconditioning, and the control of the proportion of by-passed air bymeans of dampers, in which direct-l expansion coils are used as thecooling and dehumidifying medium, and in which the dampers are adaptedto be adjusted to vary the proportion of by-passed air by means of adevice responsive to the surface temperature of said coils, said devicecomprising setting adjustment means operatively associated with meansresponsive to the room conditions, whereby the setting of the saiddevice may automatically be altered to meet abnormal conditions, therefrigeration capacity being controlled in response to variations in theroom conditions.

These and other objects and advantages of the present invention willappear more clearly in the course of the following description thereof.

In the drawing: I Fig. 1 is a diagram illustrating one embodiment of thepresent invention, and Figs. 2 and 3 are diagrams of portions of theplant illustrating certain modifications.

With particular reference to Fig. 1 air from the room I0 to beconditioned is drawn through a return duct I2 into a suction space I4 bymeans of a fan I6 which discharges the air into room III. The part ofthe air withdrawn from the room IIJ into the suction space I4(hereinafter referred to as recirculated air) may reach the suctionspace I4 either directly or by passing first through a refrigerating anddehumidifying zone. In the latter event, the recirculated air passesthrough an opening I8 near the end of the return duct remote from theroom I0, into a space 20, where fresh air entering through a fresh airduct 22 may be added to the recirculated air, and then passes over thedirect expansion units 24 into a mixing zone 26 immediately in front ofthe suction space I4. Alternatively the recirculated air may reach thesuction space I4, through a by-pass duct 28 which discharges into thesaid mixing zone 26. For controlling the proportion of air by-passed adamper 30 is provided in the by-pass duct 28 and a second damper 32 islocated at the air entrance to the direct expansion units. The dampersmay be of any suitable known kind, but for convenience the louvre typehas been used, in which damper 32 consists of a plurality of vanes 36pivoted between frame members 38 and adapted to be moved by an actuatingbar 40 and damper 30 consists of a plurality of vanes 33 pivoted betweenframe members 34 and adapted to be moved by an actuating bar 35. Ifdesired dampers 42, 44 may likewise be installed in the recirculated airduct I8 and in the mouth of the fresh air inlet 22 if such inlet isprovided. These additional or optional dampers 42, 44 may be manuallyadjustable whereas the dampers 30 and 32 are adapted to have theirsetting automatically adjusted in response to variations in the surfacetemperature of the refrigeration means or to a function there- Asindicated in the drawing, a direct expansion unit is connected to one ormore compressors 46a, 4Gb and 46c by means of a single suction line 48and branch suction lines 48a, 48h and 48e and to a condenser 41 by meansof a liquid line 49 through a valve 5I. Instead of using more than onecompressor for variable refrigerating capacity, a single compressor ofvariable capacity may be used. Valve 5I may be a thermostaticallycontrolled expansion valve, a refrigerant float valve or any other knownmeans of controlling the flow of refrigerant between the condenser 41and the evaporator or direct expansion unit 24. It is immaterial whethereach compressor has its separate condenser or all compressors dischargeinto one condenser as shown so long as the liquidlines of all thecondensers enter a common liquid line before supplying the directexpansion unit. There may be one or more direct expansion units so longasv they all are fed with refrigerant from a single liquid line throughone or more refrigerant control valves and the evaporated refrigerantfrom all enters a common suction line. The important factor is that ifmore than one coil is used, they are connected so that all are in usewhenever there is any refrigeration.

According to the present invention the compressors are controlled by adevice responsive to the room conditions. This may take the form of agas filled bulb 54 and a bellows 50 so connected that a rise intemperature will expand the bellows moving arm 56 and contactor 58 in aclockwise direction around axis 55, successively contacting points 60a,60h and 60e thus closing circuits and in a manner which those skilled inthe art will readily understand, successively starting compressors 66a,46h and llSc. The device described for controlling the compressors isone form of temperature control or thermostat, but the device may be anyknown form of temperature control such as a thermostat. i

The device for controlling dampers 30 and 32 so as to govern theproportion of by-pass recirculated air and conditioned air is shown as abulb 82 in contact with the surface of the direct expansion unit 2t andbeing connected to a bellows 52. The bulb contains a fluid which expandswith a rise in temperature thus distending the bellows and causing thearms to rotate in a counter-clockwise direction around axis 53, (in thedrawing) with the result that bar 40 moves upward moving damper 32 moretdward the closed position and bar 35 moves to the right carrying damper30 more towardthe open position. This device may, of course, be replacedby any known device for moving dampers in response to a sensitiveelement, such as the bulb 62, either directly or indirectly such aspneumatically, electrically or in any other form. The sensitive elementor bulb may be located in any position where it will be responsive to atemperature function of the expansion unit surface temperature.

For the better understanding of the present invention, the expressionfunction of the surface temperature of the refrigerator coils will nowbe more fully explained with reference to 26 which has been hereinbeforereferred to as the mixing zone.-

Thus the sensitive member 62 may be located as shown in Fig. 1 in closecontact with the surv face of the coils of the direct expansion unit,within the coils themselves, or the suction pipe 48 or its branches 48a,48h, 48e so as to be affected by the temperature therein, or at a pointbetween the direct expansion units and the mixing zone so as to beaffected by the temperature at that point.

As will readilyv be seen from the drawing, the system Vdescribed isdesigned to operate on the principle of maintaining substantiallyconstant the coil surface temperature of the direct expansion units byadjusting the relative proportions of by-passed air to intensivelyconditioned air in accordance with the varying values of a function ofsaid surface temperature, whereas v the capacity of the refrigeratorplant is altered in accordance with variations in room conditions. For agiven setting of the devices 50 and 52, and while the norma conditionscorresponding to such setting obtain in room Hl, the dampers 30 and 32will be adjusted so that the mixture discharged by fan i6 will maintainsubstantially constant said normal conditions. If the room l0 isuntenanted, that is to say, if there be no factor present tending todisturb the conditions obtaining therein, damper 30 will besubstantially fully open and damper 32 will be substantially fullyclosed, the compressor motors will not be operating, so that the directexpansion units will not be refrigerating and substantially the whole ofthe reclrculated air will be by-passed. If, through infiltration of heator moisture or through the occupancy of the room, the conditions thereinare slowly or more rapidly altered so as to reach a point within therange for which device 5|! has been set, the said device will respond tostart up the first compressor motor, whereupon the surface temperatureof the corresponding coils will be very rapidly lowered to within therange for which the damper control rdevice 52 is set. This will thenoperate to adjust 'the dampers so as to decrease the proportion of Fig.l to Fig. 3. In Fig. 1 the sensitive member 62 is shown in directcontact with the surface of the refrigerator, so that the function is anidentity. The word function is to be understood in the sense usuallygiven it in mathematics, so that the conditionsI for example thetemperature, inside the coils (Fig. 3) or in the air leaving the coils ashort distance away from the coils (Fig. 2) may all be said to befunctions of the surface temperature since in each case the conditionsbear some specific relationship to the said surface temperature. Forexample, the temperature inside the coils will differ from the surfacetemperature at least by the conduction gradient of the material of thecoil walls. The conditions at a point a short distance away from thecoils on the side thereof nearest to the fan i5 will have been so littledisturbed, as to make them substantially equal to those in closeproximity to the coils, and these latter obviously depend in a closemanner from the surface temperature. By a short distance away fromthecoils is meant a distance far enough to involve spatial separationbut not far enough to bring the point (or the sensitive member) withinthe influence of the stream of by-pressed air. The zone of influence ofthe by-passed air is the zone by-passed air and to increase the amountof intensively conditioned air, in order to counteract the chilling ofthe coils. The factor tending to restore the conditions in room i0 tonormal is the proportion of lintensively conditioned air, and thisdepends on the extent to which a given volume of recirculated air canmaintain the coil surface temperature within the predetermined limits ofconstancy. The capacity controlling device 50 will tend to keep thefirst compressor `motor running until normal conditions have beenrestored in room l0, but the longer the compressor motor runs the morepronounced will be the refrigeration effect in the coils, so that inorder to maintain the coil surface temperature constant, a greatervolume of recirculated air (intensively conditioned air) will berequired. Hence the damper control device 52 will continue to close thedamper 30 and to open damper 32 until the volume of intensivelyconditioned air is such that equilibrium is established. In thesecircumstances a restoring factor will be injected into room I0 but owingto the relation between the volume of the return duct and that of theroom space, a certain time will elapse before normal conditions arefully restored or until a point is reached at which the capacitycontrolling deconditioned air to be governed not by room conditions butby the coil surface temperature of ditioning has passed. If thecondition disturbing factor in room I is such that its effectscontinually increase, then a point will be reached at which the device50 will operate to connect a second compressor motor in circuit so thatfor this second compressor the same sequence of events will hold good inrelation to the dampers and the damper controlling device as wasdescribed for the rst motor. Thus it will be seen that the second, andsimilarly the third or any other stage, compressor motor will be runningand resting for reasonable periods which do not give rise toobjectionable results so far as the motors are concerned. At the sametime, the damper controlling device 52 by actuating the dampers asdescribed will ensure that the motors are running for only the minimumtime consistent with economy and satisfactory air conditioning.

'I'he device 50 will control the capacity of refrigeration and thedamper controlling device will ensure that such capacity will beefficiently utilized to secure the desired correct proportion of latentto sensible heat.

Iclaim:

l. In an air conditioning system comprising a room to be conditioned. areturn duct for recirculated air having a spent air inlet end and aspent air discharge end, a mixing zone, a refrigerating anddehumidifying zone communicating with said mixing zone, a fancommunicating on its suction side with said mixing zone and on itsexhaust side with said room, said return duct communicating with itsspent air inlet end with said room and with its discharge end with saidrefrigerating and dehumidifying zone on the sde thereof remote from saidmixing zone to direct recirculated air through saidrefrigerating anddehumidifying zone, direct expansion refrigeration means in saidrefrigeration and dehumidifying zone adapted to treat recirculated airand comprising compressors and' motors to drive said compressors, aby-pass connecting said return duct with and defining said mixing zoneand 'adapted to by-pass untreated recirculated air, a

by-pass baffle on said by-pass a main baille between said spent airdischarge end and said refrigerating means, means including meansresponsive to a function of the surface temperature of saidrefrigerating means operatively associated with said by-pass baille andsaid main baille to vary the relative positions thereof in response tovariations in said function and means including means responsive to roomconditions operatively associated with said motors to vary the capacityof said refrigerating means in response to room conditions.

2. The method of Ventilating and conditioning a room which includeswithdrawing air from the room, conditioning said air by causing it topass over the surface of a direct expansion refrigeration means ofvariable capacity, adding bypassed withdrawn air of a differentcondition to said conditioned air and adjusting in response to airconditions in the room the capacity of the vrefrigeration means andadjusting in response to a function of the surface temperature of saidrefrigeration means the proportion of bypassed withdrawn air andconditioned air and delivering this mixture of bypassed withdrawn airand conditioned air to the room in order to vary the conditions in theroom.

3. The method of Ventilating and conditioning a room which includeswithdrawing air from the room, conditioning said air by causing it topass over the surface of a direct expansion refrigeration means ofvariable capacity, vadding bypass withdrawn air of a different conditionto said conditioned air and adjusting in response to air conditions inthe room the capacity of the refrigeration means and adjusting inresponse to a function of the surface temperature of said refrigeratlonmeans the proportion of bypassed withdrawn air and conditioned airand'delivering this mixture of bypassed withdrawn air and conditionedair to the room in order to vary the conditions in the room.

4. In an air conditioning system comprising a room to be conditioned, areturn duct for recirculating air having a return air inlet end and areturn air discharge end, a mixing zone, a refrigerating anddehumidifying z one communicating with said mixing zone, a fancommunieating on its suction side with said mixing zone and onitsdischarge side with said room. said return duct communicating withits return air inlet end with said room and with its discharge end withsaid refrigerating and dehumidifying zone on the side thereof remotefrom said mixing zone; direct expansion refrigeration means in saidrefrigeration and dehumidifying zone adapted to treat recirculated airand comprising compressors and motors to drive said compressors, abypass connecting said return duct with `and ydefining said mixing zoneand adapted to bypass untreated recirculated air, a bypass baille onsaid bypass, a main baille between said return air discharge end andsaid refrigeration means, means including means responsive to a functionof the surface temperature of said refrigerating means operativelyassociated with said bypass baille and said main baille to vary therelative positions thereof in response to variations in said functionand means including means responsive to room conditions operativelyassociated with said motors to vary the capacity of said refrigeratingmeans in response to room-

